Alveolar tract

Local host defenses of both the upper and lower respiratory tract, along with the anatomy of the airways, are important in preventing infection. Upper respiratory defenses include the mucodliary apparatus of the nasopharynx, nasal hair, normal bacterial flora, IgA antibodies, and complement. Local host defenses of the lower respiratory tract include cough, mucodliary apparatus of the trachea and bronchi, antibodies (IgA, IgM, and IgG), complement, and alveolar macrophages. Mucus lines the cells of the respiratory tract, forming a protective barrier for the cells. This minimizes the ability of organisms to attach to the cells and initiate the infectious process. The squamous epithelial cells of the upper respiratory tract are not ciliated, but those of the columnar epithelium of the lower tract are. The cilia beat in a uniform fashion upward, moving particles up and out of the lower respiratory tract. 

Upper respiratory tract irritation can occur from inhalation of a medicinal gas, vapor, or aerosol. For assessing the potential of an inhalant to cause URT irritation, the mouse body plethysmographic technique (Alarie, 1966, 1981a, b) has proven to be extremely usefid. This technique operates on the principle that respiratory irritants stimulate the sensory nerve endings located at the surface of the respiratory tract from the nose to the alveolar region. The nerve endings in turn stimulate a variety of reflex responses (Alarie, 1973 Widdicombe, 1974) that result in characteristic changes in inspiratory and expiratory patterns and, most prominently, depression of respiratory rate. Both the potency of irritation and the concentration of... 

From a drug delivery perspective, the components of the host defence system comprise barriers that must be overcome to ensure efficient drug deposition as well as retention in and absorption from the respiratory tract. Important non-absorptive clearance mechanisms include mucociliary clearance, alveolar macrophages and metabolism (Figure 6.2). 

The sites of action and effects of ozone and other photochemical oxidants are described in Chapters 8 and 9. Recent work with primates has suggested that ozone is absorbed along the entire respiratory tract, penetrates more into the peripheral nonciliated airways, and causes more lesions in the respiratory bronchioles and alveolar ducts as the inhaled ozone concentration increases from 0.2 to 0.8 ppm. The most common and most severe tissue damage was observed in the respiratory bronchioles. The ciliated cells in the terminal bronchioles and the Type 1 cells in the epithelial layer of the proximal alveoli of rats were the... 

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